The present invention relates generally to methods and apparatus for lifting. More specifically, the present invention relates to methods and apparatus for lifting elongated objects, such as tubing or pipe.
The invention can be used with any type of elongated member made from any material, including solid members such as rods. Additionally, despite being described at times below as related to the oilfield and drilling industry, the invention is not so limited and can be used in any industry.
The drilling and production of hydrocarbon wells involves the use of large quantities of tubing, including pipe as a component of a drillstring and casing used to line the well. Normally, this tubing is available in sections of twenty to forty feet in length. These individual sections are then connected together to form the drillstring or casing tubing. A standard hydrocarbon well drilled on land may employ thousands of feet of drill pipe and tubing, requiring thousands of individual joints of tubing and pipe to be handled while drilling the well. An deep water offshore well may require considerably more pipe or tubing.
The individual sections of tubing are normally transported from a fabrication facility to the well site by truck or supply boat. The tubing must then be moved from the truck or boat to the drilling rig in a safe and secure manner. Some tubulars, such as pipe, have threaded pin ends and box ends, which help prevent the pipe from being damaged during transport. Because of the large number of tubulars used in drilling a well, the handling of these tubulars is of great concern in the operation of a drilling rig.
One method utilized in handling tubulars has been simply to use a harness or sling to wrap around the tubular in a “choker” configuration and lift the tubular by the sling. Lifting from a single point lift, as described above, requires a great deal of effort in properly locating the lift point near the center of mass of the tubular so that the tubular remains balanced during the lift. This method is not favored because of the inherent risk to men and material should the tubular not be lifted in a balanced manner.
Another method involves using a lifting appliance having hooks that are designed to grasp into the ends of a tubular. The hooks are typically connected via wires to a centralized lifting point. These hooks are inserted into the open ends of a tubular and bear against its inside surface. This type of lifting hook has been known to cause damage to the tubular interior or threaded connections, particularly when the interior of the tubular is coated. If damaged, the tubular often has to be trimmed down to remove the damaged area.
Another method involves metal end caps placed over each end of the tubular. The caps are typically connected via wires to a centralized lifting point. These metal end caps commonly have an elongated body with a solid plate attached to one end. Attached to the body is a lifting lug that can then be coupled to a central lifting point. These metal end cap assemblies surround the entire end portion of the tubular and prevent the damage often caused by lifting hooks. One drawback of these metal end cap assemblies is their weight, especially for larger diameter pipe. The heavier the end cap, the more difficult to handle. Another drawback with such assemblies is they allow metal to metal contact with the pipe, which can damage the pipe. Metal lifting appliances are also subject to corrosion and maintenance problems, especially in offshore applications.
Additionally, a general problem in pipe lifting is the requirement by some drilling contractors that the thread protectors on the ends of the tubular be “non-liftable.” This requirement stems from the fact that many present lifting devices, such as lifting hooks, damage the interior of the tubular. Accordingly, thread protector manufacturers needed to design and manufacture a protector that prevented such damage. This was accomplished by sealing the end of the protector, in some instances with a cover (such as a metal plate), so that lifting hooks could not be inserted into the interior of the pipe. This increases the costs of protectors and, more importantly, cannot guarantee that personnel handling the pipe will not break open through the cover and insert a lifting hook. Applicants' invention obviates the need for a “non-liftable” protector and ensures that the interior of the pipe is not damaged during the lifting process.
Thus, there remains a need in the art for methods and apparatus for safely and efficiently lifting tubulars, or other objects, in a manner that does not damage the tubular or object. Therefore, the embodiments of the invention are directed to methods and apparatus that seek to overcome these and other limitations of the prior art.